The present invention relates to a photosensitive printing plate which is suitable for the production of printing forms for use in flexographic printing.
It is known to produce letterpress or flexographic printing forms by imagewise exposure of light-hardenable, in particular, photopolymerizable layers and washing out the non-hardened layer areas by means of an appropriate solvent. Photosensitive materials of this type are described, for example, in DE-A 22 15 090 and DE-A 29 42 183.
Photosensitive flexographic printing plates usually comprise a multilayer material. In most cases, they are formed of a dimensionally stable support, an adhesive layer, a photopolymerizable or photocrosslinkable elastomeric layer, a non-tacky covering layer and a detachable protective film.
The support may be made of a metal or, preferably, of a dimensionally stable, transparent plastic film. It serves to reinforce and maintain the dimensional stability of the, optionally up to several millimeters thick, elastomeric layer in the printing process. To obtain firm anchoring of the light-hardenable layer to the support an adhesive layer is required, which comprises, for example, a polyurethane or polychloroprene-based one-component or two-component adhesive, as described in DE-A 31 00 175, DE-A 31 07 741, DE-A 24 44 118 and DE-A 31 37 416, a polymerizable layer (US-A 3,036,913) or a mixture of polyvinyl chloride and polyvinyl acetate (DE-A 33 19 676). EP-A 64 564 discloses mixtures of specific polyesters and polyamides, polyurethanes or polyolefins, which are used for the same purpose.
Bonding of the elastic photopolymerizable layer to the support with the aid of solid polymer layers is, in general, effected by hot-laminating at temperatures which cause the adhesive-promoting polymer layer to melt.
Many of the known adhesive layers produce bonds of insufficient strength. When the laminate is heavily stressed during the production or use of the printing form, the flexographic printing layer may become detached from the support.
In the application of two-component adhesives, which has frequently been described, the usually poor storability of the raw materials and the limited pot life of the mixture have a disadvantageous effect. Cured two-component adhesives are, moreover, often difficult to dissolve and, consequently, cleaning of the coating equipment becomes difficult and expensive. In addition, strongly crosslinked layers melt at relatively high temperatures, such that high laminating temperatures are required, which may damage the photopolymer layer.